What is the difference between game theory and machine learning?
These are big areas, so here is a brief description of the differences:

Game theory is concerned with studying solutions for 'games', which are basically a set of decisions leading to certain outcomes. In game theory you look at strategies to achieve the best outcome for a given participant. One classic example (which isn't really a game in the traditional sense) is the Prisoner's Dilemma: you and your friend have been arrested, and if only one of you testifies against the other, that person gets a reduced sentence, and the other one a much longer one. If you both testify against each other, you both get a medium sentence, and if you both keep quiet, you both go free. You don't know what your partner in crime does, so do you a) testify, or b) keep quiet? If you keep quiet, you might go free if your partner also keeps quiet, but if he testifies, you are in it for a long time. So it's risky to keep quiet, even though you get the better outcome. If you testify you might avoid a longer sentence, but also will not go free. What is your best choice?

Game theory is often used in economics to model behaviour, as a rational agent would try to optimise gains.

Machine Learning, on the other hand, is a way of training a statistical classifier. You feed features into an algorithm, and the algorithm then gives you a certain output, depending on the data you have trained it with. This hasn't got anything to do with game theory per se, but I guess you could use machine learning to train an algorithm to choose moves in a game situation and then compare how that matches the optimal choices according to game theory.

As I said, this is a very brief comparison. For more details I suggest you follow the links to read up on those two fields.

UPDATE: Now that the papers are accessible &mdash; game theory is indeed used as a benchmark. In the first paper, the rational agent assumption from game theory is being modeled, but without a human expert telling the algorithm what that means. So you learn (using deep learning) what it means to be rational. In the second paper the authors attempt to learn a better algorithm than tit-for-tat, and indeed use game theory as a theoretical framework for comparison/evaluation.